This invention relates to a magnetic recording medium and a method for the manufacture of the same. More particularly, it relates to a disk-shaped magnetic recording medium comprising a magnetic layer containing needle magnetic powder and binder on a flexible nonmagnetic substrate, and a method for the manufacture of this medium.
A variety of disk-shaped magnetic recording media have seen practical application as floppy disks. With such media, recording and playback are conducted by bringing the magnetic head into circumferential sliding contact with the disk while the disk is being rotated. If magnetic particles should be oriented in a fixed direction in the magnetic layer of the medium, maximum and minimum outputs will occur in alternation with rotation of the disk, giving rise to the fluctuations in output known as modulation.
This modulation is caused by such factors as the degree of orientation of the needle magnetic particles. Too high a modulation is undesirable in practical applications as this prevents the accurate reading of information recorded on the medium. Percent modulation is normally computed with the formula: EQU (A-B)/(A+B).times.100%
where A is the track average of the maximum amplitude and B is the track average of the minimum amplitude.
There exists also another type of output fluctuation called high-pass modulation, which depends primarily on the surface smoothness of the medium. As shown in FIG. 1, this is an output fluctuation ratio predominantly determined by the track average of the difference between maximum amplitude A' and minimum amplitude B'. The high-pass modulation too should be as low as possible.
As already noted above, disk-shaped media normally rotate at a high speed of at least several hundreds of revolutions per minute, and in some cases several thousands of revolutions per minute while sliding over the front face of a magnetic head. The result is rapid wear and degradation of the medium, which can be a major factor behind a decline in reliability. There is a strong demand for improved durability of the medium. Many attempts have been made for enhancing durability, but to a less satisfactory extent.